A satellite navigation system, e.g., a global positioning system (GPS), allows satellite navigation receivers, e.g., GPS receivers, to determine their locations and velocities according to satellite signals. The GPS may include a constellation of more than 24 GPS satellites orbiting the earth. There can be at least four GPS satellites visible at a given time and a given place on the earth surface. Each GPS satellite continuously broadcasts GPS signals at a predetermined frequency. The GPS signals contain time and orbital information of the satellites. A GPS receiver can receive the GPS signals transmitted from at least four GPS satellites synchronously. Based on the time and orbital information of at least four GPS satellites, geographical coordinates of the GPS receiver including latitude, longitude, and altitude can be calculated.
Nowadays, vehicles and electronic devices such as personal digital assistants (PDAs) and cellular phones can be equipped with GPS receivers. The GPS receiver can include multiple acquisition channels and tracking channels, and can work in a boost state or in a normal state. In the boost state, all the acquisition channels and tracking channels are enabled to acquire and track the GPS satellites. If more than four satellites are tracked, the GPS receiver can be switched to the normal state. In the normal state, only one or two channels may be enabled. If some GPS signals of the tracked GPS satellites are lost, the GPS receiver can be switched back to the boost state. However, the conventional GPS receiver has relatively high power consumption.